1. Field of the Invention
The present invention relates to a motor that moves a movable body such as a door, a sunroof, a passenger seat, or a gate, and to a body moving apparatus that includes the motor.
2. Description of the Related Art
Some vehicles, passenger cars or vans, have a sliding door on one or more sides of the body, and a sliding-door motor is employed to open and close the sliding door. A driving mechanism couples the sliding-door motor and the sliding door. The driving mechanism includes a drum fixed to a driving shaft of the sliding-door motor and that rotates with the shaft, a door-closing wire for closing the sliding door and a door-opening wire for opening the sliding door couple the drum and the sliding door.
A door switch is provided in the compartment of the vehicle and the door switch is electrically coupled with the sliding-door motor. An opening operation for opening the sliding door and a closing operation for closing the sliding door is performed by operating the door switch. The door switch is provided nears the driver seat or near the front passenger seat, or can be integrated in a door handle or a key. A conventional art has been disclosed in, for example, Japanese Patent Application Laid-Open No. H9-125823.
Assume that a vehicle with a sliding door is standing on a slop, with front side down and back side up, and the sliding door is opened in this state. In this case, the sliding door opens forcefully due to gravity force acting on the sliding door.
Similar problem occurs when closing the sliding door when the vehicle is standing in a state with front side down and back side up.
Some conventional sliding-door motors include brake coils to solve the above problem. Such a sliding-door motor includes a rotor rotatable about a rotation shaft, a stator disposed around the rotor, a field magnet holder provided in the stator to hold field magnets, a coil holder disposed on the rotor, and a conducting coil provided on the coil holder, where the rotor is rotated (the field magnet holder and the coil holder are rotated relative to each other) by magnetic field generated according to application of a voltage to both ends of the conducting coil (conducting to the conducting coil), rotation of the rotor is transmitted to the driving shaft and the drum is rotated in a forward/backward direction, so that the sliding door is opened/closed. Thus, the sliding door motor includes not only the conducting coil but also a brake coil provided on the coil holder to be stacked on the conducting coil, and it also includes a brake circuit formed by connecting both ends of the brake coil using a conducting wire. In this sliding door motor, when magnetic field is generated on the conducting coil by application of a voltage across the both end, an induced electromotive force occurs between the both ends of the brake coil and a current flows in the brake circuit so that magnetic field is generated in the brake coil. Because the magnetic field generated in the brake coil reduces intensity of the magnetic field generated when a current flows in the conducting coil, it can suppress a relative movement of the field magnet holder and the coil holder to control a moving speed of the sliding door.
In the sliding door motor including the brake coil, even if the door switch is operated in a vehicle where the vehicle is inclined, a moving speed of the sliding door can be suppressed so that a problem of the sliding door opening forcefully is prevented, and a problem that the door closing forcefully can be prevented. Especially, in the sliding door motor including the brake coil, since a change rate of magnetic field intensity per unit time acting on the brake coil increases according to increase of a rotation number per unit time of the rotor, magnetic field intensity of magnetic field generated in the brake coil by an induced electromotive force increases so that a force suppressing a moving speed of the sliding door acts largely. Therefore, a force that suppresses a moving speed of the sliding door and obtained by the brake coil acts largely on a steep slope. Accordingly, a moving speed of the sliding door can be controlled even on a steep slope.
However, there is a problem in the conventional sliding door motor that, when the sliding door is operated for opening or operated for closing using the sliding door motor, the rotation of the rotor is suppressed by the brake coil, so that the efficiency of the sliding door motor is reduced.
This problem also occurs, for example, in a sliding door motor that opens and closes a back door (a door) provided on a rear portion of a vehicle, or a motor for operating a sunroof provided at a ceiling of a vehicle.
Thus, there is a need of a motor for a movable body better efficiency and operability.